Today's microprocessors typically use cooling fans mounted to the processor package to ensure that the processor continues to operate within acceptable temperature limits. If the cooling fan should ever fail, or if other circumstances arise that cause the internal temperature of the processor to exceed a maximum acceptable limit, then a typical processor will assert a thermal trip signal that indicates to the rest of the computer system that the processor has overheated. The processor will then enter a halt state and system operation will cease.
A problem may arise as processors are manufactured with smaller and smaller transistor dimensions. As transistor dimensions decrease, the leakage currents increase dramatically. In the case discussed above where a processor has entered a halt state following an assertion of the thermal trip signal, if the leakage currents of the processor exceed the ability of the processor package to dissipate heat, then the processor's die temperature will continue to increase. As the die temperature increases, the leakage currents increase even more. This spiral continues until the temperature increases to the point where the circuits on the die are damaged.